Physics Results from RHIC

1
Physics Results from RHIC
Gunther Roland
XLIII Cracow School of Theoretical
Physics Zakopane 5/30-6/7 2003
2
Exploring QCD with Heavy Ions
Early Universe
II
Temperature (MeV)
Quark-Gluon Plasma

• Structure of Relativistic Nuclei
• Mechanism of Entropy Production
• QCD phase diagram
• Properties of QGP

I
III
200
Critical Point
IV
Phase Boundary
Hadron Gas
Atomic Nuclei
0
0
1
Matter Density mB (GeV)
3
Two Lectures
I. Bulk Production
II. Hard Scattering
Charged Hadron pT-Spectrum in AuAu at
RHIC (PHOBOS)
4
Bulk Production
Hard Scattering
5
Initial State
Final State Interactions
6
Control Parameters sqrt(s)
Drees, QM01
Different sqrt(s) dependence of soft vs hard
processes
7
Control Parameters Centrality
Spectators
Participant Region
b
2R 15fm
Spectators
Smaller Impact Parameter b
More Participants (Npart) Wounded Nucleons
Bigger Collision System
8
Control Parameters Centrality

• Centrality controls
• Volume (Npart)
• No. of binary collisions (Ncoll)
• Shape of interaction region
• Npart vs Ncoll
• soft vs hard processes
• coherent vs incoherent production

9
Relativistic Heavy Ion Collider

• First Physics in 00
• Versatile machine
• AuAu (00-02)
• 19.6 GeV
• 56 GeV
• 130 GeV
• 200 GeV
• pp (02,03)
• 200 GeV polarized
• dAu (03)
• 200 GeV

• 4 Experiments
• 2 big
• 2 small
• Complementary capabilities

10
STAR

• Large acceptance tracking detector
• Mass, charge and momentum for gt1000 hadrons per
  event

11
PHENIX

• High Rate, Particle ID, Triggering
• Rare particles Leptons, High pT

12
PHOBOS

• Full Acceptance Multiplicity Detector
• High precision spectrometer near y0 (low pT)

13
BRAHMS

• Particle Production at small angles
• High resolution spectrometer good particle ID

14
Part I Bulk Particle Production
15
Predicted Multiplicity for RHIC
Central AuAu (200 GeV)
600
1200

• Extrapolate
• AA at 20 GeV
• pp at 200 GeV

Compilation by K. Eskola
Rapidity Density
16
4-p Multiplicity at RHIC
BRAHMS PLB 523 (2001) 227, PRL 88 (2002) 202301
BRAHMS
130 GeV
BRAHMS
200 GeV
dN/dh
PHOBOS nucl-ex/0210015
200 GeV
19.6 GeV
130 GeV
PHOBOS
PHOBOS
PHOBOS
dN/dh
Pseudo-rapidity
17
Result vs Predictions
Central AuAu (200 GeV)

• Multiplicity at low end of range
• Most models didnt do so well

600
1200
Rapidity Density
Color Glass
18
Limiting Fragmentation
BRAHMS
PHOBOS
BRAHMS PRL 88 (2002) 202301
PHOBOS nucl-ex/0210015

• Study shape in rest-frame of one nucleus
• Distributions fall on limiting curve at large h
• Limiting curve is unique for each centrality bin

19
?Nch? scaling vs Npart

• Nch proportional to Npart

20
?Nch? scaling vs Npart

• Nch proportional to Npart

Constant of proportionality Nch in ee- at same
sqrt(s)
21
Total Multiplicity vs. Beam Energy
PHOBOS QM02, Steinberg
22
Rapidity Distributions at 200 GeV
PHOBOS QM02, Steinberg
q
q
200 GeV Central AuAu
ee- measures dN/dyT(rapidity relative
tothrust axis)
yT
h
AA/pp 1.4-1.5
Surprising agreement in shape between AA/ee- /pp
23
Particle density near midrapidity
PHOBOS QM02
24
Centrality Dependence at h lt 1
AuAu
200 GeV
130 GeV
19.6 GeV preliminary
_
pp
Saturation model works from 20 to 200 GeV
25
What is the Energy Density?
Central AuAu (200 GeV)
600
1200

• 650 1GeV/(p R2 1 fm/c) 4 GeV/fm3

Much bigger than ecrit
if we have fast thermalization!
Rapidity Density
26
Azimuthal Anisotropy
Head on view of colliding nuclei
Peripheral
Central
Initial State Anisotropy Coordinate Space
27
Anisotropy v2 vs Centrality
STAR
? lt 1.3 0.1 lt pt lt 2.0
PHENIX
Up to mid-central collisions, v2 reaches hydro
limit
28
Hydrodynamics and v2
Teaney, Lauret, Shuryak, nucl-th/0110037
Kolb, Heinz, nucl-ex/0204061

• Data consistent with hydro calculations
• Sensitivity to EoS

29
Hydro Equation of State
Kolb, Heinz, nucl-ex/0305084
30
Hydrodynamics and Spectra
Kolb, Rapp, Phys. Rev. C 67 (03) 044903
Parameters ?0 0.6 fm/c s0 110 fm-3 s0/n0
250 TcritTchem165 MeV Tdec100 MeV
31
Blast wave fit

• Blast wave
• Hydro-inspired Fit
• Parametrize Final State
• Local thermal equilibrium (T)
• Linear radial flow profile rx,y(r)
  r0,x,y r
• Geometrical size rx and ry
• Freeze-out time to and duration Dto

Even better than the real thing
32
Blast wave Fits to Spectra
Simultaneous Fit to p,k,p gives Kinetic
Freeze-Out Temperature, Transverse Expansion
velocity
33
Blast wave Fit to Correlation Data
Consistent Data from STAR, PHENIX, PHOBOS Also
HBT vs reaction plane Unlike
particles Balance Functions Short-lived
Resonances Consistent Results Lifetime 10
fm/c Particle emission over few fm/c
Fabrice Retiere SQM 03, Mike Lisa
34
Hydro and Correlation Data
Kolb, Heinz nuclt-th/0305084
Hydro calculation underestimates size,
overestimates time
35
Statistical Model Fit
Relative Abundances Two Parameters (or three or
four) ! Caveat Resonances, Phase-space
over/under population
36
Tchem vs Tkin
Florkowski, Broniowski, nucl-th/0212052
Addition of resonances may allow freezeout with
Tchem Tkin
c.f. Torrieri, Rafelski, nucl-th/030507
37
Physics Results from RHIC Lecture II
Gunther Roland
XLIII Cracow School of Theoretical
Physics Zakopane 5/30-6/7 2003
38

• Memento Bulk Particle Production _at_ RHIC
• Saturation consistent w/ multiplicity systematics
• Final state anisotropy indicates Thermalization
  Energy Density gt 5 GeV/fm3
• Momentum distributions and correlations are
  hydro-like, with a large radial flow field
• Hydrodynamic calculations show sensitivity of
  results to EoS many qualitative features
• Timescales are very short Thermalization,
  Expansion, Freeze-out

39
2nd Lecture
I. Bulk Production
II. Hard Scattering
Charged Hadron pT-Spectrum in AuAu at RHIC
40
Dense Matter Diagnostics
Jet cross-section calculable in QCD
Leading Particle
41
Dense Matter Diagnostics
Study fate of jets in dense matter in AuAu
Jet cross-section calculable in QCD
Leading Particle
Leading Particle
42
STAR AuAu
Opal ee-
43
Dense Matter Diagnostics
Study fate of jets in dense matter in AuAu
Jet cross-section calculable in QCD
Leading Particle
Leading Particle
Poor mans jet Leading Particles
44
Charged Hadron Spectra
Results from all RHIC experiments!
45
Control Parameters Centrality

• Total yield scales with Npart
• Volume-scaling lt-gt Coherence
• Expect Ncoll scaling for hard (point-like)
  processes
• Incoherent production

46
Jet Quenching at High pT
expected
protonproton
observed
AuAu
Yield at high pT in AA is 6 times smaller than
expected
47
Jets in Dense Matter
Leading Particle

• Are we really looking at jets?
• Look for jet structure by measuring
• small angle correlations
• back-to-back correlations
• relative to high pT leading particle

48
Peripheral AuAu data
D. Hardtke QM 02

• Jets seen in peripheral AuAu and pp
• Azimuthal correlations
• Small angle (Df 0)
• Back-to-Back (Df p)

49
Central AuAu data
D. Hardtke QM 02

• Disappearance of back-to-back correlations in
  central AuAu
• Away-side particles absorbed or scattered in
  medium

50
Jet suppression via Energy Loss
Vitev, Gyulassy, PRL 89 (2002)
Suppression due to the energy loss of fast
partons in plasma via induced gluon radiation
51
Centrality Dependence of Suppression
Central
STAR Preliminary
Peripheral
52
Another Look at Centrality Dependence
PHOBOS, nucl-ex/0302015
approximate Npart-scaling at intermediate pT !?
53
Npart Scaling in Saturation Model
Kharzeev, Levin, McLerran, hep-ph/021332
High pT suppression as an initial state
effect Parton saturation breaks incoherence
54
Experimental Test dAu
Vitev, nucl-th/0302002, Phys.Lett.B in press
Vitev and M.Gyulassy, Phys.Rev.Lett. 89 (2002)
Central
Peripheral
Prediction for RHIC
Fixed target pA data
55
Experimental Test dAu
Central
Kharzeev, Levin, McLerran, hep-ph/021332
56
Preliminary Results for dAu
STAR Preliminary

• Min-bias dAu data from PHENIX/STAR, relative to
  pp
• Similar to low-energy data (Cronin effect)
• No suppression

57
Centrality dependence of RdAu
58
Back-to-back Jets in dAu
dAu
AuAu
59
Preliminary Lesson from dAu

• Back-to-Back Jets are observed
• Data compatible with extrapolation of
  Cronin-effect to RHIC
• No suppression effects seen
• If data holds Jet quenching indicative of
  light parton energy loss (2-3 GeV) in a dense
  medium
• Some high-pT puzzles remain -gt

60
Instant Thermalization
E. Shuryak, nucl-th/0112042
Peripheral
Limit (lmfp 0)
v2
S. Voloshin, QM02
Central
61
Proton puzzle
dN/dpT(p) dN/dpT(p)
62
Suppression for light/heavy hadrons

• High-pT hadrons from fragmentation of fast
  partons
• Suppression/energy loss should effect all hadrons
• But No suppression for baryons at 2 lt pT lt 4
  GeV/c

63
Baryon v2

• At high-pT
• Baryon anisotropy exceeds that for mesons
• Also seen for p vs p

64
New (old) Idea Recombination
Lopez, Parikh, Siemens, PRL 53 (1984) 1216
Fries, Mueller, Nonaka, Bass, nucl-th/0301087 Grec
o, Ko, Levai, nucl-th/0301093 Molnar, Voloshin,
nucl-th/0302014
Fragmentation

• Dense partonic medium
• Hadron production by quark recombination
  (coalescence)
• Fries et al Favorable relative to fragmentation
  for thermal parton momentum distribution

Recombination
65
Recombination/Fragmentation
66
Recombination and v2

• Looking per quark
• Common behavior for Baryons/Mesons
• Do we see partonic flow?
• Gluons? Entropy?

67
Recombination/Fragmentation and v2
Bass, CIPANP 03
68
Recombination/Fragmentation and Spectra
Bass, CIPANP 03
69
Summary Lecture II

• Extensive data sets for intermediate/high pT
• Observation of several unique effects
• Violation of collision scaling
• Large elliptic flow (Baryons vs Mesons)
• Proton puzzle
• New data (dAu) and new ideas (recombination)
• Suggest were looking at
• Energy loss of fast partons in dense partonic
  matter
• Collective flow of partonic matter